1. Field of the Invention
This invention relates, in general, to electrical apparatus and, more specifically, to instrument transformers, such as current transformers.
2. Description of the Prior Art
In conventional current transformers, it is common practice to encapsulate a magnetic core and coil assembly in a resilient, elastomeric composition, such as butyl rubber or various epoxy resins. Although such materials provide excellent dielectric properties, they have become quite expensive. In addition, the process of molding these types of materials around the current transformers is very time consuming since it generally takes several hours for these materials to cure to a hardened state. Furthermore, with these types of encapsulating materials it has been difficult to provide a fluid-tight seal between the molding material surrounding the core and coil assembly and the secondary terminal assembly which extends through the outer layer of molding material.
It has been proposed to injection mold a layer of insulating material around current transformers. Such a process simplifies the manufacturing operation since the current transformer is encapsulated in a hardened insulating material in a matter of several minutes instead of the several hours required with conventional types of encapsulating processes. Since extremely high pressures are used in the injection molding process, it has heretofore been difficult to prevent the molding material from covering the secondary terminal assembly and, further, it has been impossible to insure an adequate fluid-tight seal between the outer layer of molding material and the secondary terminal assembly.
Thus, it would be desirable to provide an instrument transformer, such as a current transformer, having a unique secondary terminal design which enables the current transformer to be encapsulated in an insulating material through an injection molding process. It would also be desirable to provide a current transformer which has a fluid-tight seal between the molding material and the secondary terminal assembly.
A basic requirement of small instrument transformers, such as current transformers, is the use of a permanently attached shorting bar that will short out the secondary terminals when the current transformer is not in use. The shorting bar must be permanently attached to the current transformer and, further, must short out the two terminals in a conventional current transformer configuration as well as three terminals in the case of a secondary tapped design on a dual voltage current transformer. In addition, the shorting bar should interlock with a terminal cover in order to prevent the cover from being installed if the shorting bar is in the wrong position.
Thus, it would be desirable to provide a secondary terminal assembly for a current transformer which includes an improved shorting bar which is easily adaptable for two and three terminal current transformer configurations. It would also be desirable to provide a secondary terminal assembly for a current transformer having a shorting bar which meets the requirements of permanent attachment to the current transformer as well as providing an interlock feature with the terminal cover.